Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
  • C04B40/0028—Aspects relating to the mixing step of the mortar preparation
  • C04B40/0039—Premixtures of ingredients
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
  • C04B14/02—Granular materials, e.g. microballoons
  • C04B14/04—Silica-rich materials; Silicates
  • C04B14/06—Quartz; Sand
  • C04B14/062—Microsilica, e.g. colloïdal silica
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
  • C04B2103/0068—Ingredients with a function or property not provided for elsewhere in C04B2103/00
  • C04B2103/0082—Segregation-preventing agents; Sedimentation-preventing agents

Definitions

• the present invention relates to aqueous suspensions comprising precipitated silica and their use in the preparation of compositions based on cement or similar mineral binder or compositions derived therefrom.
• cement composition means a composition based on cement or any other similar mineral binder, and of water. These compositions constitute products which are used as such, in particular as a coating, or which are intended to incorporate in particular mineral fillers of variable particle size.
• compositions containing a mineral binder and a mineral filler in the form of aggregates are generally considered to be concrete.
• compositions of concrete for structural work must meet specific requirements in dobby of:
• concrete can either be produced on site or produced in a plant and transported to the site of use (ready-mixed concrete). So that the composition can retain acceptable properties, even for a short period, it must be ensured stability in the hydrated state, in particular by preserving its fluidity intact or by limiting the segregation of suspended matter. More specifically, the architectonic concretes, that is to say the visible elements, must also satisfy aesthetic requirements:
• Precast concrete for the production of facade elements, pavers, floors, pipes must more particularly have a low permeability to gases and liquids for optimal durability, as well as the same aesthetic qualities as architectural concrete for visible elements.
• compositions of mortars or plasters for the finishing work must also meet a certain number of specific requirements: good water retention for avoid the water leaving by penetration into the porous support or by preferential drying on the surface (risk of cracking and fa ⁇ nage on the surface);
• critical parameters are the fluidity to ensure the implementation, the bleeding rate or the adhesion to the support, the water retention.
• a fluidifying agent can improve the fluidity of a composition, but the high contents sometimes necessary to achieve the desired result very clearly promote bleeding and reduce the setting kinetics and therefore the acquisition of mechanical resistance at young ages (fight against cracking, formwork ability, early commissioning ).
• setting retarders making it possible to preserve and transport a composition for a certain time after its preparation, also have a very marked effect on the bleeding and setting kinetics.
• the present invention proposes to meet this demand for improved additives making it possible to combine several advantageous properties among those mentioned above.
• the object of the invention is to provide a new additive for cementitious compositions or derivative compositions which makes it possible to reduce the bleeding and segregation effects of concrete compositions.
• the object of the invention is also to provide an additive making it possible to combine improved fluidity, good water retention, even in the case of high contents of water and / or in fluidifying or plasticizing agents, and to ensure the hardened product has good durability, in particular a reduction in permeability to water and to gases, making it possible to reduce efflorescence.
• the subject of the invention is an aqueous suspension comprising a mixture of at least one aqueous suspension of precipitated silica and at least one latex, in which said aqueous suspension of precipitated silica has a dry matter content of between 10 and 40% by weight, has a viscosity less than 4.10 ⁇ : Pa.s for a shear this 50 s " and produces after centrifugation at 7500 rpm for 30 minutes a supernatant containing more than 50 c of the weight of the silica initially in suspension.
• the first essential component of the mixture forming the aqueous suspension which is the subject of the invention is an aqueous suspension of precipitated silica with a high dry matter content, having a low viscosity and good stability over time.
• the dry matter content of said suspension is between 15 and 35% by weight.
• the viscosity of said suspension is advantageously less than 4.10 "2 Pa.s for a shear of 50 s " 1 .
• suspensions are very stable and their stability can be assessed by means of a sedimentation test which consists in centrifuging said suspen ⁇ sion at 7500 rpm for 30 minutes.
• the amount of silica contained in the supernatant obtained at the end of this centrifugation represents more than 50%, preferably more than 60% of the weight of the silica contained in the suspension.
• the quantity of silica contained in the supernatant obtained after centrifugation represents more than 70%, in particular more than 90% of the weight of the silica in suspension.
• Another characteristic of these suspensions relates to the particle size of the silica particles in suspension.
• silica suspensions concen ⁇ trated up to now known in addition to their high viscosity, have the drawback of having large agglomerates in suspension which induce sedimentation over time.
• the particle size distribution of suspended matter can be defined using the median ⁇ iameter D 50 , which is the grain diameter such that 50% of the population of grains in suspension has a smaller diameter.
• D 35 represents the grain diameter such that 95% of the population of grains in suspension has a smaller diameter.
• F D Another characteristic size of the suspensions is the deagglomeration factor F D. This factor, all the higher as the silica suspension is deagglomerated, is indicative of the rate of fines, that is to say the rate of particles of size less than 0.1 ⁇ m which are not detected by a granulometer. current.
• the particle size characteristics of the silica suspensions are determined by means of a particle size measurement carried out on the suspensions, using a SYMPATEC granulometer.
• F D is measured by introducing into a granu ⁇ lometer a known volume V of diluted suspension so as to obtain a silica content of 4% by weight and is equal to the ratio (10 x V in ml / optical concentration detected by the granulometer) .
• silica agglomerates present in these suspensions are small.
• the particle size distribution of the agglomerates in suspension is such that their median diameter D 50 is less than 5 ⁇ m and the deagglomeration factor F D is greater than 3 ml.
• the diameter D is less than 2 ⁇ m, the factor F D is greater than 13 ml and in addition, the diameter D 95 is less than 20 ⁇ m.
• the second essential component of the mixture forming the aqueous suspension which is the subject of the invention is a latex, namely an aqueous suspension of particles of natural or synthetic resin.
• said particles are products of polymerization of at least one ethylenically unsaturated monomer.
• the latex itself is obtained from the emulsion polymerization of at least one ethylenically unsaturated monomer.
• the ethylenically unsaturated monomer may advantageously be chosen from styrene, butadiene, acrylic acid, methacrylic acid, esters of acrylic or methacrylic acid, preferably C1-C12 esters, vinyl esters , and mixtures thereof.
• the latex which can be used according to the invention can thus comprise particles of homopolymer or else copolymer resin, an example being a styrene-butadiene rubber latex.
• the size of the latex particles is variable depending on the intended application. In a first advantageous embodiment, this size is 0.1 to 5 ⁇ m. Mention may in particular be made of latexes whose particle size is from 0.1 to 0.3 ⁇ m, preferably styrene / butadiene latexes, or else latexes whose particle size is from 1 to 5 ⁇ m, preferably latexes. acetate / versatate. In a second advantageous embodiment, this size is at most 100 nm; these nanolatexes can be very varied in nature.
• the aqueous suspension according to the invention comprises from 3 to 25 parts by weight of silica, expressed in dry weight, per 100 parts by weight of suspension, more advantageously from 5 to 20 parts by weight of silica per 100 parts of suspension.
• the dry weight of the latex represents the value of 5 to 50 parts per 100 parts by weight of aqueous suspension according to the invention, advantageously from 10 to 40 parts per 100 parts of suspension.
• aqueous suspensions according to the invention can be incorporated into cementitious pastes or more generally cementitious compositions, based on mineral binder and water, to which they provide in particular resistance to segregation and water retention associated with an increase. fluidity due to a synergistic effect between the silica suspension and the latex.
• the invention therefore also relates to compositions based on a mineral binder and water, characterized in that they comprise an aqueous suspension as defined above.
• the mineral binder can be of any known type, in particular PORTLAND CPA HP cement, CPA 55, CPJ 45, CPA CEM I, CPA CEM I PM, CPA CEM I PMES, CPJ CEM II, CPJ CEM II PM, CPJ CEM II PMES, CHF CEM II, CLK CEM II, blast furnace slag or pozzolanic binders.
• the ratio of water to binder is variable and depends above all on the fluidity desired for the composition. This ratio can in particular be from 0.3 to 2, preferably from 0.3 to 1.5.
• the silica in these compositions, it is preferable for the silica to represent from 0.3 to 5% by weight relative to the binder, expressed in dry weight ratio, preferably from 0.8 to 1.5%. It is also advantageous for the dry weight of the latex to represent the value of 0.2 to 50% by weight relative to the binder, expressed in dry weight ratio, preferably from 3 to 30%.
• the compositions can also comprise at least one fluidifying agent. This agent can be chosen from the substances commonly used for this purpose in cementitious compositions.
• lignosulfonates casein, polynaphthalene, in particular polynaphthalene sulfonates of alkali metals, melamines, polymelamms, formaldehyde derivatives, polyacrylates of alkali metals, polycarboxylates of alkali metals and polyoxide of grafted ethylene.
• Such an agent can advantageously be used in an amount of 0.1 to 10% by weight relative to the binder.
• This agent can be introduced separately from the aqueous suspension according to the invention, or else simultaneously by means of a suspension comprising both the suspension of silica, the latex and the said agent.
• compositions can also comprise at least one water retaining agent, which can be chosen from the substances commonly used for this purpose in cement-based compositions. It will advantageously be chosen from polyvinyl alcohols optionally modified, polyethylene glycols, polyoxyethylenes, acrylic polymers, in particular polyacrylamides, polysaccharides of bacterial origin, such as xanthan gum, guar gums, cationized guar gums, extracts of carob seed, alginates, pectins, celluloses, cellulose ethers, in particular carboxyalkyl celluloses, alkylceiiuloses, hydroxyalkylcelluloses, such as methylhydroxypropylcelluloses, polyvmylpyrrolidone, sugars, in particular dextrose, ⁇ bose, corn starches, cationized or non-cationic wheat, lignites, leonardites and alkalinylate derivatives, polyacrylates and polystyrenesulfonates.
• Such an agent can advantageously be used in an amount of 0.01 to 10% by weight relative to the binder.
• compositions can also advantageously comprise a setting accelerator, such as aluminum sulphate, in a content of 0.01 to 3% by weight relative to the binder (expressed as dry weight ratio).
• a setting accelerator such as aluminum sulphate
• this content is expressed by weight of anhydrous aluminum sulphate.
• This agent can be introduced separately from the aqueous suspension according to the invention, or alternatively by means of a suspension comprising both the silica suspension, the latex and said agent.
• Reinforcement fibers will also advantageously be used in the compositions, making it possible to improve the resistance to cracking.
• These fibers are preferably chosen from polyvinyl alcohol, polypropylene, polyethylene, steel, polyacrylonitrile, cellulose, carbon, kevlar, polyamide and polyester fibers.
• the cementitious compositions based on a mineral binder and water which have just been described can be used as such or combined with other materials, in particular for forming compositions of concrete (or mortar).
• concrete means the mixture of a binder mineral, water and aggregates of varying granulometry, in particular gravels, sands and possibly ⁇ e fine, or even ultra-fine.
• the invention also relates to concrete compositions comprising an aqueous suspension previously described.
• These compositions can be obtained by mixing the suspensions according to the invention with an inorganic binder, aggregates and optionally additional water, or else by mixing a cementitious composition described above with aggregates and optionally additional water.
• the invention therefore also relates to the use of aqueous suspensions or cement compositions described above in concrete compositions, in particular specialty concretes of the aforementioned types and renderings.
• aqueous suspensions or cementitious compositions meeting at least one of the preferred characteristics indicated above with regard to the relative contents of silica and latex, and optionally in fluidifying agents or water retaining agents, and where appropriate in cement.
• the proportion of aggregates in these concrete compositions can be chosen in a manner known per se from the usual ranges corresponding to the type of concrete desired.
• the invention finds a particular application in so-called specialty concretes which must exhibit particular properties of surface appearance, mechanical resistance, durability of the finished product, fluidity during processing and low tendency to the segregation.
• concrete fluids concretes for the manufacture of slabs (cement screeds and fluid mortars for screeds), submarine concretes which must be easily pumpable and injectable, facing concretes, concretes prefabricated by centrifugation or hot pressing, plasters surface smoothing and leveling, especially of floors, colored concretes, which must have a homogeneous surface without efflorescence and a relatively clear base color, as well as light concretes, concretes for industrial floors, waterproof concretes and concrete cementing of oil wells, which must have a reduced porosity, all these concretes seeing their properties improved thanks to the invention.
• the high fluidity which is often desirable is achieved thanks to the invention, while improving the water retention capacity of the compositions, which makes it easier to set up and to reduce the cracking problems due to a water departure resulting in a plastic shrinkage soon after installation.
• a subject of the invention is therefore the use of the aqueous suspensions described above as a water retention agent in cementitious compositions or in concretes. This use, which reduces plastic shrinkage and consequently cracking, is particularly advantageous for cement screeds and smoothing plasters.
• the invention also has for object the use of aqueous suspensions as defined above, as an anti-segregation agent in cement compositions based on a mineral binder and water and in concrete compositions, in particular in compositions where the weight ratio water / cement or more generally water / binder is from 0.3 to 2, preferably from 0.3 to 1.5.
• the invention is also very advantageous for the production of prefabricated facing concretes or waterproof concretes, because it makes it possible to obtain better dispersion of the cement, better homogeneity. This improves the surface appearance in terms of regularity and durability of the cured product thanks to the limited penetration of water and gases. In the case of facing products, smoothing and leveling coatings, this is accompanied by a lightening of the color and an improvement in the surface appearance, better resistance to carbonation and a limitation of the appearance of efflorescence, as well as a reduction of the corrosion of the reinforcements.
• the invention is also concerned with the use of aqueous suspensions previously described as an agent reducing the permeability to gases and liquids in compositions based on a mineral binder and water or in concrete compositions. .
• Resistance to water penetration is a decisive advantage for the waterproofing of works located in a floodable or humid zone or of works intended to receive water (reservoirs, dams, aqueducts, swimming pools, water pipes) ).
• a precipitated silica cake Gl is prepared in the following manner. In a stainless steel reactor equipped with a propeller stirring system and a jacket heating:
• the silicate concentration (expressed as S ⁇ 0 2 ) in the base is then 85 g / 1.
• the mixture is brought to 79 ° C. while keeping it under stirring.
• the temperature of the reaction medium is 79 ° C. for the first 25 minutes, then it is brought from 79 ° C. to 86 ° C. in 15 min, and then maintained at 86 ° C. until the end of the reaction.
• the total duration of the reaction is 118 min.
• a precipitated silica slurry is obtained which is filtered and washed using a filter press so that a Gl silica cake is finally recovered, the loss on ignition of which is 78% (therefore a dry matter content 22% by weight) and whose Na 2 S0 4 content is 1% by weight.
• the G2 suspension of silica obtained is characterized by:
• This suspension is perfectly stable with respect to sedimentation for more than three months. It contains approximately 10% by dry weight of silica and 26% by dry weight of latex.
• a concrete composition is prepared according to the following formula:
• the aggregates are introduced and kneaded for one minute, then the cement is introduced and kneaded for 30 seconds. Then, while mixing, water and the fluidizer are introduced, along with 42.5 kg (10% relative to the cement) of the aqueous suspension of the reference example.
• the amount of silica added corresponds to 1% of the weight of cement introduced.
• the water / cement weight ratio of this concrete composition is therefore 0.41.
• a concrete composition is similarly prepared by increasing the initial water content so as to obtain a water / cement weight ratio of 0.49, the quantity of all the other constituents being kept identical.
• compositions are evaluated by pouring concrete into identical watertight molds and by demolding after three days.
• the characteristics of hardened concrete are also evaluated.
• the whiteness of the product is measured using a XENOTEST colo ⁇ meter and quantified using the chromatic coordinates L " , a ' and b * in the CIE 1976 system (L * , a * , b * ) as defined by the International Commission and listed in the Collection of French Standards (AFNOR) colorimetric color No X08-12 (1983).
• the adhesion of the concrete on a support is improved due to the presence of the silica suspension and of the latex, as well as the resistance to abrasion (reduction of dusting).
• Application example 2 Production of a cement composition with a high water content (or grout)
• This example aims to highlight the synergistic effect produced by the silica suspension and the latex on the rheological and stability properties of cementitious pastes with high water content.
• a first series of tests not in accordance with the invention is carried out, showing that silica or latex alone do not solve the problems posed by these grouts, which are compared to two tests according to
• a grout comprising a suspension of silica prepared in the same manner as in preparation example A, but without adding latex. It responds to the following formula: - HTS100 g cement
• a similar grout is prepared in the same way or the water / cement ratio is 0.35.
• the water / cement ratio is therefore 0.28.
• the preparation is analogous to Comparative Test 1, the latex being introduced in place of the silica suspension.
• a grout corresponding to the formula is prepared:
• Example A 9 silica (dry weight) i g latex (dry weight): 2.5 g
• the water / cement ratio is 0.28.
• the preparation is similar to that of the comparative tests.
• a grout similar to that of test 1 is prepared, where the water content is adjusted to obtain a water / cement ratio of 0.35.
• compositions are subjected to the following rheological measurements carried out on a RHEOMAT 115 device equipped with an MS DIN 145 cell.
• the grout is subjected to an increasing shear from 0 to 1000 s ⁇ 1 in 1 minute, then to a constant shear of 1000 s "1 for 1 minute, and the shear is decreased to 0 s " 1 in 1 minute, while measuring the viscosity. The final viscosity is noted.
• a difference between the two values is indicative of a heterogeneous cake, a lower dry extract higher than the upper dry extract signifying segregation.
• the excellent anti-bleeding and segregation properties of the additives according to the invention are completely unexpected since the skilled person would have expected a reduction in the bleeding and segregation properties by combining an aqueous suspension silica with a latex and not an improvement.
• test 1 compared to comparative test 1, there is a lesser tendency to gel, the behavior of the grout being quasi-Newtonian.
• the grout does not present any bleeding or segregation problem: it remains perfectly homogeneous in static as well as dynamic mode, although it is much more fluid than the grout of comparative test 1.
• test 2 while the W / C ratio is 0.35, the grout remains perfectly stable and homogeneous in static and dynamic mode, unlike the grout of comparative test 2.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Civil Engineering (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)
• Silicon Compounds (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Paints Or Removers (AREA)
• Adhesives Or Adhesive Processes (AREA)
• Pigments, Carbon Blacks, Or Wood Stains (AREA)

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• 1996
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